The present invention relates to a sputtering target of ferromagnetic material for use in the deposition of a magnetic thin film of a magnetic recording medium, and particularly for use in the deposition of a magnetic recording layer of a hard disk based on the perpendicular magnetic recording system; and to a sputtering target with low generation of particles which enables a stable electrical discharge when sputtered with a magnetron sputtering device since the pass-through flux is large.
In the field of magnetic recording as represented with hard disk drives, a material based on Co, Fe or Ni as ferromagnetic metals is used as the material of the magnetic thin film which is used for the recording. For example, Co—Cr-based or Co—Cr—Pt-based ferromagnetic alloys comprising Co as its main component are used for the recording layer of hard disks based on the longitudinal magnetic recording system.
Moreover, composite materials of Co—Cr—Pt-based ferromagnetic alloys comprising Co as its main component and nonmagnetic inorganic substances are often used for the recording layer of hard disks based on the perpendicular magnetic recording system which was recently put into practical application.
A magnetic thin film of a magnetic recording medium such as a hard disk is often produced by performing sputtering with a ferromagnetic sputtering target having the foregoing materials as its components in light of its high productivity.
As a method of manufacturing this kind of ferromagnetic sputtering target, the melting method or the powder-metallurgical method may be considered. It is not necessarily appropriate to suggest which method is better since it will depend on the demanded characteristics, but a sputtering target composed of ferromagnetic alloys and nonmagnetic inorganic grains, which is used for forming the recording layer of hard disks based on the perpendicular magnetic recording system, is generally manufactured with powder metallurgy. This is because the inorganic grains need to be uniformly dispersed within the alloy basis material, and this is difficult to achieve with the melting method.
For example, proposed is a method of obtaining a sputtering target for a magnetic recording medium including the steps of mixing the powder, which is obtained by mixing Co powder, Cr powder, TiO2 powder and SiO2 powder, with the spherical Co powder with a sun-and-planet motion-type mixer, and molding the mixed powder with hot pressing (Patent Document 1).
In the foregoing case, it can be observed that the target structure includes spherical phases (B) in a basis metal phase (A) in which inorganic grains are uniformly dispersed (FIG. 1 of Patent Document 1). Although this kind of structure is favorable from the perspective of improving the pass-through flux, it is not necessarily favorable as a sputtering target for a magnetic recording medium from the perspective of inhibiting the generation of particles during sputtering.
Moreover, proposed is a method of obtaining a sputtering target for a Co-based alloy magnetic film by mixing SiO2 powder to Co—Cr—Ta alloy powder prepared with the atomization method, subsequently performing mechanical alloying thereto with a ball mill to disperse the oxides in the Co—Cr—Ta alloy powder, and molding this with hot pressing (Patent Document 2).
Although the drawings are unclear, the target structure in the foregoing case comprises a shape in which black portions (SiO2) are surrounding a large white spherical structure (Co—Cr—Ta alloy). This kind of structure is also not necessarily favorable as a sputtering target for a magnetic recording medium.
In addition, proposed is a method of obtaining a sputtering target for forming a thin film for use in a magnetic recording medium by mixing Co—Cr binary alloy powder, Pt powder and SiO2 powder, and hot pressing the obtained mixed powder (Patent Document 3).
Although the target structure in the foregoing case is not shown in the drawings, it is described that the observation result was that there are a Pt phase, a SiO2 phase and a Co—Cr binary alloy phase in the target structure and a diffusion layer exists around the Co—Cr binary alloy layer. This kind of structure is also not necessarily favorable as a sputtering target for a magnetic recording medium.
There are various types of sputtering devices, but a magnetron sputtering device comprising a DC power source is broadly used in light of its high productivity for the deposition of the foregoing magnetic recording film. This sputtering method is to place a positive electrode substrate and a negative electrode target opposite each other, and generate an electric field by applying high voltage between the substrate and the target under an inert gas atmosphere.
Here, the sputtering method employs a principle where inert gas is ionized, plasma composed of electrons and positive ions is formed, the positive ions in this plasma collide with the target (negative electrode) surface to discharge the constituent atoms of the target, and the extruded atoms adhere to the opposing substrate surface to form a film. As a result of performing the sequential process described above, the material configuring the target is deposited on the substrate.
[Patent Document 1] Japanese Patent Application No. 2010-011326
[Patent Document 2] Japanese Laid-Open Patent Publication No. H10-088333
[Patent Document 3] Japanese Laid-Open Patent Publication No. 2009-1860